Banca de DEFESA: SAMIR DO NASCIMENTO VALCÁCIO
Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.STUDENT : SAMIR DO NASCIMENTO VALCÁCIO
DATE: 17/12/2020
TIME: 09:00
LOCAL: Videoconferencia - https://cutt.ly/6fcqwHK
TITLE:
Thermal effect provoked by the Ediacaran Umarizal pluton over rocks of the Seridó Group
(RN): structural, mineralogical and petrophysical implications
KEY WORDS:
Umarizal pluton; thermal aureole; Ediacaran; Borborema Province; NE Brazil.
PAGES: 144
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUMMARY:
The northeastern portion of the Borborema Province (PB), in northeastern Brazil, is marked by a voluminous Ediacaran magmatism that intrudes the paleoproterozoic gneiss-migmatitic basement (the Caicó Complex) and neoproterozoic metasupracrustal rocks (the Seridó Group). In this context, the Umarizal pluton, the focus of this work, is classified among the Ediacaran types as the Charnockite alkaline suite (AlcCh). The main objective of this research is the reevaluation of previous interpretations through new field data concerning emplacement mechanism, dating plutonic rocks and of neosome of thermally affected hosting units and thermal modeling of magma cooling. The obtained results showed that the magmatic suite is composed of three distinct petrographic facies, where the Umarizal and Ação facies are restricted to the Umarizal pluton and the Lagoa facies is found as minor bodies intruding in the Tourão pluton. Usually the AlcCh Suite is composed of quartz-syenite and quartz-monzonite and their charnockitic equivalents. Structurally, the main pluton is emplaced between the NE-SW Portalegre and NE-SW Frutuoso Gomes shear zones. Field criteria suggest that these lineaments had progressive movements, begining with synistral extensional that favoured the emplacement of the Umarizal magma and finished with dextral contractional movement. Synchronously with the emplacement, a thermal aureole of up to 1-2 km thick was formed in Formação Jucurutu country rocks, with Buchan-type metamorphic associations, registered in andaluzite - sillimanite in paragnaisses, scapolite in calciosilicatic gneisses and flogopite in marbles. The U-Pb age of 583 ± 1.8 Ma, obtained in zircons from a neosome, is similar, within error, to the zircon U-Pb ages of the Tourão (589.3 ± 4.4 Ma) and Umarizal (565 ± 22 Ma) plutons. Modal and lithogeochemical compositions configure two suites, one of probable mantle derivation (gabbro-norites, anorthosites) and another crustal-derived (granites and charnoquites), thus characterizing an anorthosite - mangerite - rapakivi-granite – granite magmatic association. The mineralogical variation from the least differentiated facies to the most evolved facies suggests the dominance anhydrous conditions (fayalite, hyperstene, diopside-hedenbergite) at the beginning of crystallization to water subsaturated at the end of evolution and, thus, favouring the formation of hornblende and biotite. The initial crystallization conditions of the charnockite suite indicate control by the fayalite-magnetite-quartz buffer, with pressures of ~ 9 kbar and temperatures in the order of 900-1100 ° C. On the other hand, geothermobarometric data using Al-in hornblende allowed to calculate approximate conditions of 4.5 ± 0.6 kbar and 755 ± 32 ° C for the final crystallization stage. The integration of mineralogical and petrophysical data of the plutonic units and the thermal aureole allowed the thermal modeling of the cooling magma, being coherent with conditions of high geothermal gradient (40 °C / km), peak of thermal metamorphism in 15,000 - 80,000 years after emplacement, and thermal conditions extending to 1 - 2 km away from the contact. Considering the existence of countless other batholithic bodies of the same age in this part of the PB, it is proposed that the Ediacaran was a period of extensive crustal heating under conditions of high geothermal gradient, possibly due to the heating driven by underplating of mantelic (gabbro-norite) magmas.
BANKING MEMBERS:
Interno - 2042352 - FREDERICO CASTRO JOBIM VILALVA
Externo ao Programa - 346468 - JOSE ANTONIO DE MORAIS MOREIRA
Externo à Instituição - RICARDO IVAN FERREIRA DA TRINDADE - USP
Externo à Instituição - SERGIO PACHECO NEVES - UFPE
Presidente - 350630 - ZORANO SERGIO DE SOUZA